1. Field of the Invention
The present invention generally relates to a radial-winding stator of a motor and, more particularly, to a radial-winding stator of a motor in which said stator can be used in a single phase motor having an outer rotor.
2. Description of the Related Art
FIGS. 1 and 2 show a conventional eight-pole radial-winding stator 9 of a motor. The radial-winding stator 9 includes a main body 91 and eight magnetic pole portions 92 extending outwards from main body 91. Each magnetic pole portion 92 forms a magnetic pole 921 and a pole piece 922. An enamel copper wire can be wound around pole piece 922 to form a coil 93. The pole piece 922 includes an outer surface serving as a magnetic end face 923. The magnetic end face 923 is in the form of an arched face and has an arc length S9. The arc length S9 is determined by an angle θ9 and a radius R9. The arc length S9 is the occupied angle of pole piece 922 along the entire circumference of the stator. The radius R9 is the distance between a center of main body 91 and the outer surface of pole piece 922. A similar embodiment of the radial-winding stator 9 of the motor is. disclosed in Taiwan Patent No. M240726.
When coils 93 are electrified, magnetic field can be generated at magnetic pole portions 92, leading to the generation of magnetic lines of force. However, only a part of the magnetic lines of force, which links with a permanent magnet of a rotor (not shown), contributes to the rotational torque of the motor. Specifically, only the magnetic lines of force, that are emitted by the part of coils 93 radially aligned with magnetic end faces 923, contribute to the rotational torque of the motor. The magnetic lines of force, that are emitted by another part of coils 93 radially misaligned with magnetic end faces 923 (the uppermost and lowermost parts 931 of coils 93 where the enamel copper wire bends), does not contribute to the rotational torque of the motor. In this regard, when the number of turns of coils 93 is increased in order to provide a larger magnetic force, the parts 931 of coils 93 also become larger. As a result, the parts of coils 93 that do not contribute to the rotational torque of the motor become larger, making it difficult to improve the efficiency of radial-winding stator 9.
On the other hand, the conventional stator 9 has a height limit. Specifically, magnetic end face 923 has a height “L9” along an axial direction of main body 91. The total value of the height. “L9” and the heights of the parts 931 of coils 93 should be smaller than or equal to a maximal allowable height “H” of radial-winding stator 9. In this regard, when the parts 931 of coils 93 become larger, the total height of the parts 931 also becomes larger. Disadvantageously, the height “L9” of magnetic end face 923 becomes smaller, adversely reducing the quantity of the silicon steel plates. In other words, when the number of turns of coils 93 is increased in order to produce a larger magnetic field, the parts 931 of coils 93 will inevitably become larger. When the volume of the parts 931 of coils 93 is increased to a certain extent, the operational efficiency of the motor can no longer be improved by increasing the quantity of the silicon steel plates.
In light of this, in order to prevent the motor from having low operational efficiency due to an excessive number of turns of winding, the ratio of arc length S9 to height “L9” is designed to have a minimum value of 0.5 and a maximum value of 2. This achieves a balance between the operational power and efficiency. However, as more and more electronic products and delicate instruments are equipped with motors, there has been an increasing demand for miniaturized and compact motors. In this regard, height “L9” will be too large if the ratio of arc length S9 to height “L9” is between 0.5 and 2. Disadvantageously, the produced motors cannot be used in miniaturized motors and will not meet the market needs.
In conclusion, when the parts 931 of coils 93 become larger, the magnetic lines of force that can contribute to the rotational torque of the motor will become less and the quantity of the silicon steel plates cannot be increased, leading to a limited operational efficiency of the motor. Furthermore, since the conventional radial-winding stator 9 requires the ratio of arc length S9 to height “L9” to be between 0.5 and 2 in order to achieve a balance between the operational power and efficiency, the radial-winding stator 9 cannot be used in a miniaturized motor. Thus, it is necessary to improve the conventional radial-winding stator 9.